This invention relates to an apparatus for withdrawing small quantities of gases from the soil for later laboratory analysis. More particularly the invention relates to an apparatus which may be purged of all contaminating gases prior to withdrawing the soil gas sample thereby providing a more accurate analysis of the gases present in the soil.
The contents of a soil gas sample may indicate the presence of hydrocarbon deposits nearby. Due to the small quantity of gas collected from the soil, it is imperative however that any analysis include only those gases present in the soil itself. U.S. Pat. No. 4,261,203 discloses a soil probe having a movable tip for covering and uncovering inlet ports in the lower end of the probe. When the probe is inserted into the ground, the inlet ports are uncovered and soil gas is withdrawn into a vacuum type container. The movable tip prevents atmospheric gases from entering the probe after the vacuum container is attached; however, the probe lacks any closure means at the outlet end of the probe to allow pre-purging of contaminant gases prior to attachment of the vacuum container. U.S. Pat. No. 2,141,261 by Clark discloses a soil probe utilizing a removable vacuum container. The Clark patent also lacks a means for sealing the upper end of the probe from the outside atmosphere to allow purging of the probe. Therefore any soil gas collected in the vacuum container is contaminated by gas present in the probe when the soil gas sample is collected.
My invention, on the other hand, teaches that pre-purging of the probe prior to withdrawing a test sample is necessary to remove any gas remaining in the probe which would contaminate the test sample. Unlike my invention, pre-purging of the prior art apparatuses is impossible, however, because the prior art lack any means for sealing the upper end of the probe when the vacuum or evacuated container is removed from the probe.